There exists a great need for improving the chemotherapy of malignant tumors. To date, tumors were treated mainly by antineoplastic chemotherapeutic drugs, among them in particular the antimetabolites, alkylators and intercalating substances, as well as biosynthetic products. Since these preparations affect not only tumor cells but also other rapidly growing systems of the organism, for instance blood-forming centers, skin- and adhering structures, mucosa and germ epithelium, the therapeutic success is limited by undesirable effects.